This invention relates to raise drills and, in particular, to a chuck and wrench assembly portion for such an apparatus, which engages the drill pipe and enables pipe sections to be added or removed.
Raise drilling is a term which relates to a technique of boring or reaming large diameter holes which includes drilling a relatively small diameter pilot hole into earth strata until the cutting bit emerges into an open space and then replacing the small cutting bit with a specially-designed large-diameter cutting head or reamer and cutting the larger hole along the path of the pilot hole by pulling the reamer back toward the drill rig. This technique is well known in the art and many such drill rig apparatuses have been developed.
The subject invention relates to two other applications filed on the same day herewith, Ser. Nos. 038,574 and 051,578, entitled "Raise Drill Apparatus" and "Convertible Raised Drill Apparatus," respectively. These applications are incorporated herein by reference for additional background information.
The chuck of a raise drill apparatus operates to engage and transmit torque to the drill pipe. During up-reaming operations, lengths of drill pipe must be removed as the thrust cylinders reach the upper limit of their travel range. A wrench mechanism is normally provided to cooperate with the chuck for removing the uppermost drill pipe section.
In all known prior art the chuck and wrench mechanisms are connected to the output shaft of a transmission so that any moment loads transmitted to the chuck are reacted by the transmission output shaft and other chuck components. Although a joint has been incorporated in several known chuck mechanisms which can absorb this moment load within narrow design limits, if the design angle is exceeded the moment will still be transmitted to the drive shaft which can cause ultimate failure and result in costly delays and repairs.
Further, if the drive shaft should fail there is nothing left to support the drill pipe and cutter head and prevent them from dropping down the shaft.